Hohenzollern Castle is a hilltop castle located on Mount Hohenzollern, an isolated promontory of the Swabian Jura in Baden-Württemberg, Germany. It was constructed in three separate phases, starting with the original castle built by the Counts of Zollern in the 11th century. By the end of the 18th century it had fallen into disrepair and was demolished. The current castle, which is the third phase, was constructed from 1846 to 1867 as a family memorial by King Frederick William IV of Prussia. It contains artifacts of Prussian history, including the Crown of Wilhelm II and a letter from George Washington thanking Baron von Steuben for his service in the American Revolutionary War. Today, the castle receives over 350,000 visitors per year.